Well, greater success in northern Spain is possible, if Zaragoza surrenders, then Charlemagne's defeat by the Basques would be prevented. This could see interesting consequences with a Frankish/Carolingian state possible in Spain, and an earlier re-Chistianisation of Iberia.
Elsewhere, it is possible that he could come to the aid of his Avar vassals against the Bulgars. If he successfully shattered Bulgaian power here, this would completely change Balkan dynamics and would greatly aid the Byzantines later on. Immediatly, it could lead to a direct annexation of the upper Danube, and a reinforcement of Carolingian power in souther Germany.
This would all be aided if he avoided conflict with Eastern Rome.